RPM slow to drop to idle

[deepblueE34]

Hi Gentlemen,

I have a problem that was hoping someone here may help me with.

I drive a 520i M50 and the car accelerates fine as far as I can tell. The problem is that when I disengage the (manual) gearbox the RPM hangs at 1100 for few seconds before dropping to idle. It has not been always like that. I think the issue started after my mechanic did some work on the throttle body. I suspected an air leak and my mechanic inspected the engine for air leaks and changed the rubber throttle boot since it had a crack (according to him) but that didn't help. Now he says it is a problem with the throttle body.

What could it be? Has anyone come across these symptoms? Please share your experience here if you have.

Thanks,

 

[moots]

bro...the issue started when yr mech fiddled with the TB......only yr mech knows what he has done.go back to him.

 

[deepblueE34]

Hi moots,

Thanks for the reply. My mechanic seems genuinely clueless. Do you know what could cause the throttle to behave like this? It use to be fun to drive, now it doesn't feel right

I will try to check it with another mechanic.

 

[moots]

well,to move fwd we need to know what was done to the TB by the mech....

Sent from my GT-I9070 using Tapatalk 2

 

[deepblueE34]

Here is an update.

Finally took it to another "bmw specialist" . He said could be one of two things throttle cable or ICV. I have been wanting to change the throttle cable for some time because it looks pretty bad, so I thought lets give it a shot. Long story short after 5 hours (mostly waiting for parts), a 2nd hand ICV, a new throttle cable and some carburetor cleaner (~RM450), the issue persists . I'm very disappointed.

Today on one occasion at the traffic light the RPM surged all the way to 4K and stayed there until I had to kill the engine. This is a new symptom. I went back to the "BMW specialist" and he suggested I leave the car with him to give him a time to diagnose the problem. I will skip my "bwm specialist" rant for now .

My old mechanic says it could either be the MAF sensor or throttle body.

I'm stumped. What else should I try?


PS. Does anyone here have an extra MAF that I can borrow to test with? And while we are at it, how about an M50B20TU ECU (siemens)? That would be great!

 

[deepblueE34]

Finally, RESOLVED!

I just changed my throttle body and my idling/RPM is back to its good self.

Here is a summery of the problem and how it was fixed.

Problem:

• RPM indicator gets stuck at 1.3-.1.5K RPM for few seconds after car comes to a halt and when disengaging gear
• Engine moves very slowly to its idle speed and gets stuck momentarily on its way there
• Engine idles at 800 RPM and sounds louder than it should
• Acceleration seems to be slightly impeded

What didn't help (maybe did but unnoticeable):

• Changing ICV to a second-hand one after cleaning it
• Changing accelerator cable
• Changing TPS to a second-hand one
• Cleaning MAF sensor with MAF cleaner
• Adding injector cleaner to gas

What helped:

• Installing used throttle body after cleaning it with TB cleaner

Behavior after fix:

• Car RPM indicator moves smoothly (no stops) to its idling speed (~650 RPM) when coming to a halt
• RPM varies when disengaging gear and shifting

 

[moots]

lesson learnt bro....tb it is....

Sent from my GT-I9070 using Tapatalk 2

 

[XXX8315]

noted...

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